Ryanair B738 near Manchester on Jan 14th 2017, control inputs to prevent overspeed cause two injuries

Last Update: May 10, 2018 / 16:34:23 GMT/Zulu time

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Incident Facts

Date of incident
Jan 14, 2017

Classification
Report

Airline
Ryanair

Flight number
FR-3247

Departure
Stuttgart, Germany

Destination
Manchester, United Kingdom

Aircraft Registration
EI-EBW

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Ryanair Boeing 737-800, registration EI-EBW performing flight FR-3247 from Stuttgart (Germany) to Manchester,EN (UK) with 89 passengers and 6 crew, had been enroute at FL400 (above the jet stream) and reached the top of descent into Manchester. The flight crew initiated the descent at 0.77-0.78 mach about 109nm before Manchester, the FMC had computed the vertical profile, the autopilot and authrust were engaged, the autopilot's modes were LNAV and VNAV PATH. When the aircraft descended through FL392 the windspeeds began to increase, descending through FL367 the speed increased by 22 knots within 28 seconds and the speed trend vectors showed the predicted IAS in the overspeed area, the airspeed increased from about 0.77 to 0.818 mach into the overspeed range, the speed trend already showing a predicted airspeed 15-20 knots into the overspeed. In order to prevent the aircraft go further into the overspeed range, the captain disconnected the autopilot and pulled back on the yoke intending to pull the aircraft smoothly out of the overspeed range. However, the pilot pulled about 42lbs on the yoke causing marked changes of acceleration, two flight attendants working in the aft galley fell to the floor. The aircraft continued for a safe landing in Manchester.

The AAIB released their bulletin concluding the probable cause of the accident was:

The serious injuries suffered by a cabin crew member occurred because significant manual control inputs were applied in response to an impending overspeed, which resulted in the aircraft manoeuvring abruptly. An increasing headwind associated with a jetstream had caused the airspeed to rise. The narrow speed margins and handling sensitivities of the aircraft at high altitudes were contributory factors.

The AAIB reported one flight attendant received a fracture of her ankle and summarized the testimony by the commander (31, ATPL, 4,997 hours total, 4833 hours on type): "The commander reported that he was aware of the possibility of encountering a jetstream in the descent, but had not seen the airspeed increase to this extent before. He perceived that there was startle effect11 in his response due to both the rate of the airspeed increase towards MMO, and by the magnitude of the impending overspeed indicated by the speed trend vector. At the time, he believed he was managing the manoeuvre gently but with hindsight he suspected that startle effect caused him to exert more force on the control column than intended."

The AAIB analysed:

The FCTM highlights that the primary response to an aircraft overspeed is to use the speed brake, and that the autothrottle logic provides some overspeed protection through more aggressive speed control as the aircraft approaches VMO/MMO. The effects of this autothrottle logic had been demonstrated in the simulator to both pilots. The FCOM mentions that further overspeed protection is offered by the vertical mode transitioning from vnav path to lvl chg in conditions of impending overspeed.

The FCTM overspeed procedure also states:

‘pilots should leave the AP engaged unless it is apparent that it is not correcting the overspeed. However, if manual inputs are required, disengage the autopilot’.

The aircraft’s speed rose from 0.78 M to almost 0.82 M in 28 s. If the commander only realised the severity of the impending overspeed just before it occurred – and believed that the autopilot was not correcting the condition – then he may have felt compelled to disengage the autopilot, as described in the procedure.

Pilots are reminded during training that they must not hesitate to use a lower level of automation if required to maintain the aircraft’s flight path.

When taking manual recovery action at high altitude it is important to consider the need for careful handling. Whilst an overspeed is undesirable, there is typically a large margin between the onset of the overspeed warning and any undesired aerodynamic characteristics. Hence, there is often less risk in exceeding VMO/MMO slightly than there is in manual manoeuvring.

In this instance, the pilot considered that he was startled by the increasing speed and magnitude of the trend indication. Whilst he believed at the time that he was manoeuvring gently, the resulting overriding force on the control column was 42.76 lb – approximately double that required to disconnect the autopilot – and was large enough to cause a manoeuvre sufficient to unbalance the two cabin crew and for one to suffer a serious injury.

As well as recovery techniques for a high altitude overspeed event, some preventative measures exist, such as flying at a lower altitude, descending early, and slowing down when able do so – if necessary declining ATC requests to fly a higher speed. These activities, requiring active monitoring, may also reduce the risk of startle.

The commander commented that he learned from this experience, particularly in relation to managing the reduced operational margins and handling sensitivities of the aircraft at high altitudes.
Aircraft Registration Data
Registration mark
EI-EBW
Country of Registration
Ireland
Date of Registration
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Manufacturer
THE BOEING COMPANY
Aircraft Model / Type
BOEING 737-8AS
ICAO Aircraft Type
B738
Year of Manufacture
Qhbi Subscribe to unlock
Serial Number
Hccdk Subscribe to unlock
Maximum Take off Mass (MTOM) [kg]
Qbgfe Subscribe to unlock
Engine Count
Q Subscribe to unlock
Engine
Q nljeeAmmmhchleAh Aqq bkck Subscribe to unlock
Main Owner
Nnh fjdlpmmjlg fmjeeiAkcckd ebf djmcghmAdqqifjhndkghmfqnjj df nei Subscribe to unlock
Incident Facts

Date of incident
Jan 14, 2017

Classification
Report

Airline
Ryanair

Flight number
FR-3247

Departure
Stuttgart, Germany

Destination
Manchester, United Kingdom

Aircraft Registration
EI-EBW

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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